Lasers Boost Space Communications

Before NASA even existed, science-fiction writer Arthur C. Clarke in 1945 imagined spacecraft that could send messages back to Earth using beams of light. After decades of setbacks and dead ends, the technology to do this is finally coming of age.

This is a reliable, capable, and cost-effective optical communications technology. Optical communications technology provides data rates up to 100 times higher than today’s systems, which will be needed for future human and robotic space missions. The technology is directly applicable to the next generation of NASA’s space communications network. After the demonstration, the developed space and ground assets will be qualified for use by near-Earth and deep space missions requiring high bandwidth and a small ground station reception area.

These lasers could provide bigger pipes for a coming flood of space information. New Earth-observation satellites promise to deliver petabytes (10^15) of data every year. Missions such as the Mars Reconnaissance Orbiter (MRO) already have constraints on the volume of data they can send back because of fluctuations in download rates tied to a spacecraft’s varying distance from Earth. Laser data highways could ultimately allow space agencies to kit their spacecraft with more sophisticated equipment.

Data rates 10-100 times more capable than current RF systems will allow greatly improved connectivity and enable a new generation of remote scientific investigations as well as provide the satellite communication’s industry with disruptive technology not available today. Space laser communications will enable missions to use bandwidth-hungry instruments, such as hyper spectral imagers, synthetic aperture radar (SAR), and other instruments with high definition in spectral, spatial, or temporal modes. Laser communication will also make it possible to establish a “virtual presence” at a remote planet or other solar system body, enabling the high-rate communications required by future explorers.

As an example, at the current limit of 6 Mbps for the Mars Reconnaissance Orbiter (MRO), it takes approximately 90 minutes to transmit a single HI RISE high resolution image back to earth. In some instances, this bottleneck can limit science return. An equivalent MRO mission outfitted with an optical communications transmitter would have a capacity to transmit data back to earth at 100 Mbps or more, reducing the single image transmission time to on order of 5 minutes.

Today’s spacecraft send and receive messages using radio waves. The frequencies used are hundreds of times higher than those put out by music stations on Earth and can cram in more information, allowing orbital broadcasts to transmit hundreds of megabits of information per second. Lasers, which operate at higher frequencies, still, can reach gigabits per second. And unlike the radio portion of the electromagnetic spectrum, which is crowded and carefully apportioned, optical wavelengths are underused and unregulated. The laser, amplified by modern fiber-optic technology, achieves a power of watts compared with the tens of milli watts reached by present.

Two spacecraft set for launch in the coming weeks will carry lasers that allow data to be transferred faster than ever before. One, scheduled for take-off on 5 September, is NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE), a mission that will beam video and scientific data from the Moon. The other, aEuropean Space Agency (ESA) project called Alphasat, is due to launch on 25 July, and will be the first optical satellite to collect large amounts of scientific data from other satellites.